The invention concerns a fodder for freshwater fish, more particularly a fodder having an increased content of minerals relative to that previously described as necessary for providing fish with a good growth.
Some salmon fish are anadromous fish. Sexually mature fish migrate from seawater to freshwater to spawn, while the offspring migrate back to the sea to grow. The eggs are hatched at the river bottom, and the juvenile salmon (fry) spend their initial lifetime in the river water. In the spring, great physiological changes occur in the fry as it prepares for the transition from living in freshwater to living in seawater. The preceding autumn, when subjected to natural conditions, the fry determines whether it is large enough to migrate as smolt the next spring. In nature, the time between hatching and migrating may vary from more than one year to 5 years, depending on water temperature and food availability.
Rearing of salmon and sea trout must follow the natural mode of living for the fish. Having fertilized the eggs, the eggs are hatched in freshwater. The fish go through the yolk sack stage and the fry stage in tanks in a hatchery. In a hatchery, it is possible to manipulate both water temperature and lighting conditions, so as to control the timing of smoltification in a different manner than in nature. As such, smolt is referred to as 0-yearlings, 1-yearlings and 2-yearlings. O-yearlings are planted as smolt the first autumn after hatching in the winter, while the 1-yearlings spend more than one year in the hatchery.
After smoltification, reared fish are put into fish cages in seawater to grow until slaughtering. A daily weight increase depends on body weight and may be compared to the effect of capital size in an interest calculation. Two smolt of equal quality concerning health and physiological adaptation and planted in the sea simultaneously, may grow equally fast in terms of percentages (specific growth rate), but the larger one will reach a slaughtering size prior to the other one.
In intensive rearing of fish, the duration from hatching to smoltification, and the size of the smolt at smoltification, is of great economic importance. The size of tied-up capital, in the form of fish, is of great importance to the profitability of both the fingerling producer and the producer of consumable fish.
Rearing of salmon has become more intense. The industry has grown fast, and the need for smolt has been on the increase. Many fingerling producers are restricted in terms of withdrawing more freshwater from their water sources. This has caused the fish density in the rearing tanks of the hatcheries to increase. Among other things, this has been made possible by adding oxygen (O2) to the water. Consequently, the amount of carbon dioxide (CO2) in the water also has increased dramatically, up to as much as 40 milligrams CO2/liter (mg CO2/l) and above. The concentration of CO2 in the water depends on the water quality. Water having a low conductivity, typical of for example the coastal region of Norway, has a low buffer quality, and therefore the content of CO2 in this water becomes larger than that of more ion-rich water. Thus, watercourses in Southern and Western Norway receiving acid rain possess a water quality having conductivities down towards 10 mikroSiemens/centimeter (μS/cm). Most common in Norwegian watercourses is a water quality between 25-75 μS/cm. In comparison, regions of Eastern Norway having calcareous bedrock possess a water quality having conductivities of ca. 300 μS/cm. In order for the water to possess a certain buffer capacity, the conductivity should be above 30 μS/cm.
Fish being exposed to a high CO2-level (5 mg/l and above) over an extended time, will attain an increased level of CO2 in their blood (hypercapnia), and the amount increases with the amount in the water. This results in an increased content of bicarbonate in order to compensate for the CO2-increase, the result being that the pH-value of the blood decreases (respiratory acidosis). Fish having acidosis will seek to counteract this condition by mobilising ions from the bone structure and secrete phosphate via the kidney. A high content of CO2 in the water provide a negative influence on growth and health of the fish. Fish exposed to high CO2-levels may develop nefrocalcinosis, which is distinguished by calcium precipitating and depositing in the kidney. This is observed already at 5-10 mg/l and has been described from 15 mg/l and up (Fivelstad, S. et al.; “The effects of carbon dioxide on salmon smolt”; in “Norsk Fiskeoppdrett”, pages 40-41, no. 16, 1998).
In intensive rearing of fish, extruded fish fodder is used most commonly. This is composed of proteins, carbohydrates and fats. The protein raw materials may consist of animal protein sources, such as fish meal, bone meal, blood meal and feather meal, and of vegetable protein sources, such as soy, corn gluten, wheat gluten and lupines. Carbohydrates are primarily added as a binding agent to provide the fodder pellet with a sustainable shape and mechanical strength. The carbohydrate source may be whole or ground up wheat, potato starch or other starch sources. In order to increase the energy content of the fish fodder, animal oil, such as fish oil or vegetable oil, including rapeseed oil or soybean oil, is generally added after forming in the extruder step and the subsequent drying step. These raw materials also contain minerals. Thus, phosphate and other minerals, for example, are included in fishbone remnants of fish meal. Phosphate also is occurs as phosphate lipids in the protein sources and in the oil sources.
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.